1. Field of the Invention
This invention relates to image creating apparatuses and image display apparatuses. More particularly, this invention relates to an image creating apparatus and image display apparatus for generating and/or displaying image data approximated for representing realistic three-dimensional images, particularly when the images are displayed using polygon representation.
2. Description of the Prior Art
In conventional games of three-dimensional representation (3D), images of background objects and moving objects are merely displayed through three-dimensional image data involving three-dimensional coordinate data and textures (patterns and material feelings including colors) as if the images were photographed in a predetermined direction by a camera located at a predetermined distance.
Meanwhile, conventional games of two-dimensional representation can display images, in combination, of the background object (or background character or background picture) and the moving object (moving character or game hero character, etc.). However, the relation in position between the background object and the moving object is determined only either one of at the front or the rear of the background object with reference to the moving object. It is therefore impossible to display the background objects depicted between a plurality of background objects (e.g. between a house and a mountain or between a car and a building, or the like) in one background scene by merely setting the backward-forward relation for each background object. To this end, the conventional background image is nothing more than a mere planar image with no depth data, so that the moving object (e.g. hero character) thus depicted, upon passing between a plurality of other background objects, cannot be represented as if it passed behind or in front of or between the objects in a way of perspective representation with depth given for the objects.
FIG. 1 is a view showing an on-screen space for displaying background objects and a moving object due to a conventional technique. The example of FIG. 1 shows a case that, when rendering a person as a moving object 1 and depicting a building 2 and a tree 3 as background objects, the moving object 1 is represented in preference to the background objects. That is, the moving object 1 is set at a higher order of priority than the background objects 2 and 3. In this case, the moving object 1 is displayed as if it existed in front of the building 2 during movement from a position (a) to a position (b) and from the position (b) to the position (c), whereas it is represented at the front of the tree 3 during movement from a position (c) to a position (d). The moving object 1 in movement from the position (d) to a position (e) is displayed (solely) without superposition over the background.
FIG. 2 is a view showing an on-screen space for displaying background objects and a moving object due to the conventional technique. In an example of FIG. 2, a person is depicted as a moving object 1 and a building 2 and a tree 3 are drawn as background objects, wherein the moving body 1 is set in lower priority than the background objects 2 and 3. In this case, when the moving object 1 in movement from a position (a) to a position (b) comes to a position that is overlapped with the building 2, no representation is made for the portion overlapped with the building 2, thereby displaying the person as if he was behind the building. During movement from the position (b) to a position (d), display is similarly done. Thereafter, when the moving object 1 passes past an left end of the building 2 and further moves from the position (d) to a position (e), it is solely displayed because of the absence of the building 2 or the tree 3 there.
In the conventional art, when the moving object 1 becomes overlapped with the background object 2 or 3, nothing is done more than display only with either one of the moving object 1 or the background object 2 and 3 which is higher in priority order. This is because the data defining the depth (depth data) is not assigned to each of the background objects and the moving object.
Where a three-dimensional image is displayed on a display depending upon three-dimensional data (or polygon data; i.e. coordinate data at polygon corners X, Y, Z) for representing an object (including background objects and/or moving objects; background characters, also referred to as moving characters) constituted by gathering of a plurality of polygons, there is a necessity of representing a greater number of polygons in order to display an image with higher reality and precision. However, it takes long time for computation, as the number of polygons increases greater. There often encountered is a case where the computation for representing one frame of a three-dimensional image becomes impossible for one frame (or during vertical blanking), resulting in overburdening of processing. The resulting display image might be unnatural of movement just like frame-basis feeding. Thus, there has been a difficulty of smoothly changing in real time the three-dimensional image.
On the other hand, where the background object is displayed by combining with a moving object (hero character), there has been no setting in the forward-backward relation between the background object depicted in the background scene and the moving object. As a result, the forward-backward relation as to the background object and the moving object can not be met with the actual movement.